Buy to let mortgage up for renewal changing deeds

I'll try and make this simple my partner and his father own a buy to let house together and the mortgage is up for renewal in 15 months and we are trying to get an idea of what need to be done so we can plan. The idea is that my partner will be removed from the property so we re free to buy together. can my partners father apply for a new mortgage without my partner?can my partner be removed from the deeds at the same time? TIA